<template>
  <div class="container">
    <div class="progress-container">
      <div id="progress" class="progress" />
      <div class="circle active">1</div>
      <div class="circle">2</div>
      <div class="circle">3</div>
      <div class="circle">4</div>

      <button id="prev" class="btn" disabled>Prev</button>
      <button id="next" class="btn">Next</button>
    </div>
  </div>
</template>

<script>
export default {
  mounted() {
    const progress = document.getElementById('progress')
    const prev = document.getElementById('prev')
    const next = document.getElementById('next')
    const circles = document.querySelectorAll('.circle')

    let currentActive = 1

    next.addEventListener('click', () => {
      currentActive++

      if (currentActive > circles.length) {
        currentActive = circles.length
      }

      update()
    })

    prev.addEventListener('click', () => {
      currentActive--

      if (currentActive < 1) {
        currentActive = 1
      }

      update()
    })

    function update() {
      circles.forEach((circle, idx) => {
        if (idx < currentActive) {
          circle.classList.add('active')
        } else {
          circle.classList.remove('active')
        }
      })

      const actives = document.querySelectorAll('.active')

      progress.style.width = (actives.length - 1) / (circles.length - 1) * 100 + '%'

      if (currentActive === 1) {
        prev.disabled = true
      } else if (currentActive === circles.length) {
        next.disabled = true
      } else {
        prev.disabled = false
        next.disabled = false
      }
    }
  }
}
</script>

<style scoped>
@import url('https://fonts.googleapis.com/css?family=Muli&display=swap');

:root {
  --line-border-fill: #3498db !important;
  --line-border-empty: #e0e0e0 !important;
}

* {
  box-sizing: border-box;
}
body {
  background-color: #f6f7fb;
  font-family: 'Muli', sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  overflow: hidden;
  margin: 0;
}

.container {
  text-align: center;
}

.progress-container {
  display: flex;
  justify-content: space-between;
  position: relative;
  margin-bottom: 30px;
  max-width: 100%;
  width: 350px;
}

.progress-container::before {
  content: '';
  background-color: var(--line-border-empty);
  position: absolute;
  top: 50%;
  left: 0;
  transform: translateY(-50%);
  height: 4px;
  width: 100%;
  z-index: -1;
}

.progress {
  background-color: var(--line-border-fill);
  position: absolute;
  top: 50%;
  left: 0;
  transform: translateY(-50%);
  height: 4px;
  width: 0%;
  z-index: -1;
  transition: 0.4s ease;
}

.circle {
  background-color: #fff;
  color: #999;
  border-radius: 50%;
  height: 30px;
  width: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 3px solid var(--line-border-empty);
  transition: 0.4s ease;
}

.circle.active {
  border-color: var(--line-border-fill);
}

.btn {
  background-color: var(--line-border-fill);
  color: #fff;
  border: 0;
  border-radius: 6px;
  cursor: pointer;
  font-family: inherit;
  padding: 8px 30px;
  margin: 5px;
  font-size: 14px;
}

.btn:active {
  transform: scale(0.98);
}

.btn:focus {
  outline: 0;
}

.btn:disabled {
  background-color: var(--line-border-empty);
  cursor: not-allowed;
}

</style>
